This study was undertaken to ascertain whether 19 patients maintained on continuous ambulatory peritoneal dialysis (CAPD) for at least 1 year experienced any deterioration in peritoneal membrane function. Selected serum chemistries and skinfold measurements were also evaluated to determine whether patients dialyzed by CAPD could maintain a normal nutritional status. This study demonstrates that patients maintained on CAPD had stable dialysate protein losses, glucose absorption from the dialysate, and constant urea, creatinine, and sodium removal. When these patients were subdivided by incidence of peritonitis, the group with a lower incidence of peritonitis (one episode every 349 +/- 155 SEM days) showed stable serum protein concentration and improvement in upper arm area whereas the group with a high incidence of peritonitis (one episode every 95 +/- 7 SEM days) showed a reduction in upper arm muscle area. Thus, our data suggest that over a 1-year period, there is no deterioration in peritoneal membrane characteristics and CAPD is effective in maintaining the nutritional status of the patient. However, both membrane function and nutritional status may be impaired by frequent episodes of infection.